Stitching a picture takes a long time. I find I can do two or three hundred stitches a day. Some days I may do twice that, but my long-term daily average is close to 250. I like working 180 x 180 size pieces. That's 32,400 stitches. I can count on a project of that size taking about 130 days to complete.
As I stitch, the picture emerges. When I start I'm adding stitches to a blank canvas. The first stitch represents 100% of the completed stitches on the canvas. It's very easy to see the change in the canvas from having no stitches to having one stitch. The second and third stitches make similarly obvious changes in the canvas. As the number of stitches increases, it becomes more difficult to detect the change any particular stitch makes to the canvas. When I am in the middle of a project I often cannot see any progress after adding dozens of stitches.
Nearing the end of a project a similar phenomenon occurs. As the canvas fills with stitches, there remain fewer and fewer "empty cells." An individual stitch accounts for about .003% of the total picture, but when I'm down to the last few hundred, each stitch accounts for a much higher percentage of the stitches remaining, and it becomes easy again to see the change in the canvas that a handful of stitches makes. This gives a feeling of making faster progress.